1. Field of the Invention
The invention relates to a bi-directional clutch to be equipped on a vehicle, which is selectively automatically clutched off for putting the vehicle into a two-wheel drive mode or clutched on for putting the vehicle into a four-wheel drive mode, in correspondence to a condition of the vehicle during either forward traveling or backward traveling. The invention also relates to a vehicle equipped with the bi-directional clutch.
2. Related Art
Conventionally, there is a well-known bi-directional clutch to be equipped on a vehicle, which is selectively automatically clutched off for putting the vehicle into a two-wheel drive mode or clutched on for putting the vehicle into a four-wheel drive mode, in correspondence to a condition of the vehicle during either forward traveling or backward traveling, as disclosed in JP2003-278804A1. The disclosed bi-directional clutch comprises an input side rotor and a pair of left and right output side rotors. The input side rotor is concentrically fitted around the output side rotors through a cage holding rollers. In the normal traveling condition of the vehicle, the clutch is clutched off in such a way that the rollers are held to be separated from the inner peripheral surface of the input side rotor and the outer peripheral surfaces of the output side rotors, thereby preventing the rotary force of the input side rotor from being transmitted to the output side rotors, and thereby keeping the vehicle in the two-wheel drive mode. When the rotary speed of the output side rotors becomes smaller than that of the input side rotor during travel of the vehicle, the clutch is clutched on in such a way that the rollers are wedged up between the inner peripheral surface of the input side rotor and the outer peripheral surface of each of the output side rotors, so as to transmit the rotary force of the input side rotor to the output side rotors. Consequently, the vehicle can be automatically put into the four-wheel drive mode only when the vehicle requires an especially large traction force.
If the bi-directional clutch is used for a transaxle of an off-road type four-wheel drive vehicle, the torque is readily confined in the clutch when the input side rotor and the output side rotors are wedged with each other in a high ground-load condition. Consequently, when the forward/backward traveling direction of the vehicle in the four-wheel drive mode is changed, the rollers wedged between the inner peripheral surface of the input side rotor and the outer peripheral surface of each of the output side rotors cannot release from the input side rotor or the output side rotor. Once the problem occurs, the unexpected four-wheel drive mode is subsequently maintained, so as to reduce the fuel efficiency, and to hinder the differential rotation of the left and right output side rotors for steering the vehicle.